System and method for particles measurement

ABSTRACT

An optical system for particle size and concentration analysis, includes: at least one laser that produces an illuminating beam; a focusing lens that focuses the illuminating beam on particles that move relative to the illuminating beam at known or pre-defined angles to the illuminating beam through the focal region of the focusing lens; and at least two forward-looking detectors, that detect interactions of particles with the illuminating beam in the focal region of the focusing lens. The focusing lens is a cylindrical lens that forms a focal region that is: (i) narrow in the direction of relative motion between the particles and the illuminating beam, and (ii) wide in a direction perpendicular to a plane defined by an optical axis of the system and the direction of relative motion between the particles and the illuminating beam. Each of the two forward-looking detectors is comprised of two segmented linear arrays of detectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation application of U.S.application Ser. No. 16/652,653, filed Mar. 31, 2020, which is a UnitedStates National Stage Application filed under 35 U.S.C. § 371 ofInternational Application No. PCT/IL2018/051141 (WO 2019/082186), filedOct. 25, 2018, which claims priority and benefit from U.S. provisionalpatent application No. 62/577,403, filed on Oct. 26, 2017, each of whichis hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention is related to the field of measuring particle sizeand concentration.

More specifically, it relates to the use of optical methods formeasuring particle size and concentration, and achieving an improveddetection sensitivity or improved characterization of the measuredparticles.

BACKGROUND

Publications and other reference materials referred to herein arenumerically referenced in the following text, and are respectivelygrouped in the appended Bibliography which immediately precedes theclaims.

Many techniques exist for particle size and concentration analysis(PSA); and they can be reviewed for reference in the books “Introductionto Particle Size Analysis” by Terry Alan (1) and “Particle SizeAnalysis” by N. Stanley-Wood and Roy W. Lines (10).

The most commonly used techniques are optical, based on the interactionof the measured particles with laser radiation. Especially whenapproaching the particle size range around 1 micron and below, where Miescattering prevails, most of these techniques suffer from inaccuraciesdue to the effect of the real and imaginary part of the particle'srefractive index. It is known, for example, that in some techniques,such as techniques based on Fraunhofer diffraction analysis, lightabsorbing particles would be over-sized due to energy loss resultingfrom the absorption; while in high concentration, particles would beunder-sized due to secondary scattering, etc. Additionally, the abilityto detect individual nm scale particles is very limited as the signaldecreases according to the radius r{circumflex over ( )}6, posingsensitivity and dynamic range challenges.

An optical technique that is less sensitive to these problems is knownas Time of Transition or TOT. In this technique, the interaction of ascanning, focused laser beam and the particles is analyzed in the timedomain rather than in the amplitude domain, resulting in lowersensitivity to variation in the refractive index. A detailed descriptionof the technique appears in a paper “Improvements in Accuracy and SpeedUsing the Time-of-Transition Method and Dynamic Image Analysis ForParticle Sizing” by Bruce Weiner, Walter Tscharnuter, and Nir Karasikov(2). To a great extent, in this technique a digital de-convolutionalgorithm of the known laser beam profile from the interaction signalderives the size. The concentration is derived from the number ofinteractions per unit time within the known volume of the focused laserbeam, using principles of digital confocality.

The interaction of the particles in the TOT technique is with a focusedscanning laser beam. In order to measure smaller particles, a smallerfocused spot should be used. However, according to diffraction laws fora Gaussian laser beam, if the beam's waist is D, the divergence of thebeam is proportional to λ/D, where λ is the laser's wavelength; and as aresult the Raleigh range and the Depth of Focus decrease as λ getslarger or D smaller (Depth Of Focus is

$ {{DOF} = \frac{2\pi D^{2}}{\lambda}} ).$

The trade-off between the ability to resolve small particles, to thefocus volume and the accuracy in measuring concentration, is obvious.Thus, if the TOT technique is targeted to resolve and measure particlesin the sub-micron range, it would be limited in its ability to measurelow concentrations as the instantaneous focus volume is small and theinteraction rate of particles is low. On the other hand, taking a largerspot will improve the concentration measurement rate and its accuracy,but will degrade the quality and resolution of the size analysis.

An improvement could be achieved by using a shorter wavelength, yieldinglower divergence for a given focal spot and correspondingly a longerRayleigh range. This could have a limited effect of, as high as a factorof 2 only, since going to a too short of a wavelength will result inabsorption of the laser light by the optics and, in the case ofparticles in liquid, also potentially absorption by the liquid.

A previous patent assigned to some of the applicants of the presentapplication (U.S. Pat. No. 7,746,469, which is hereby incorporated byreference in its entirety) introduced a new technique and means tosomewhat decouple between the two contradicting requirements: theability to resolve small particles and the ability to measure lowconcentration using measurements based on single particle interactionsby means of a structured laser beam.

The method introduced in U.S. Pat. No. 7,746,469 is based on a syntheticbeam generation. The limitation as described hereinabove results fromthe inherent Gaussian beam profile of the laser beam and is somewhataddressed by the proposed synthetically generated beam where spatialresolution can be achieved in lower beam divergence. Other energydistributions could be synthetically generated and used for particlesmeasurements. One specific reference, which describes the technique, isreference (3). This publication deals with the generation ofthree-dimensional light structures used in the invention. It describesthe philosophy and the techniques used, and it also provides someexamples. In particular, the dark beam described is of primary interestfor the previous invention. Other relevant references are (4) to (9).The dark beam is a laser beam that has a dark spot or dark linesingularity at the center of a beam with an otherwise typically Gaussianenvelop. The main advantage of this beam for the purpose of PSA(Particle Size Analysis) originates from the fact that the dark centralspot/line is narrower than a classical Gaussian spot, having the samedivergence, leading to the possibility of higher sensitivity to theposition and structure of an obstructing object while maintainingsufficient volume of the Gaussian beam for concentration measurement andfor larger particles interactions as well. Dark beams can be generatedby converting a conventional laser beam with the help of an opticalelement (usually a diffractive element) or by a special design of thelaser resonator in such a way that it emits a dark beam. These lasermodes are usually members of a set called Gauss-Laguerre andGauss-Hermit modes.

Reference is made to FIG. 1 , which is a schematic illustration of achart 101 demonstrating the intensity curve of a Gaussian beam. Thehorizontal axis indicates position from the center of the beam; forexample, indicate in microns or in 10{circumflex over ( )}(−6) meters.The vertical axis indicates beam light intensity; for example, inrelative units.

In chart 101, for example, numeral 10 indicates the shape of a beam withGaussian profile; numeral 12 indicates the shape of a first lobe of aDark Beam; numeral 12′ indicates the shape of a second lobe of the DarkBeam; the two lobes are shifted in phase by 180 degrees, but this is notshown in chart 101 as this chart demonstrates Intensity; numeral 14indicates the spacing between the two lobes; as the two lobes areshifted by 180 degrees, there is a singularity with zero energy betweenthem; numeral 16 indicates the width of the beam at e{circumflex over( )}(−2) of intensity; numeral 18 indicates the spacing between thepeaks of the two lobes. FIG. 1 shows a comparison of the intensity curveof a Gaussian beam 10 with that of a dark beam generated from it. Thedark beam has two lobes 12 and 12′, and a singularity dark line 14between them. The double-headed arrows show, respectively: (i) asindicated by numeral 16, the maximum width ≅2WO of the Gaussian beam 14,where WO is the Gaussian beam waist; and (ii) as indicated by numeral18, the maximum width or the peak spacing which is ≅W0√{square root over(2)} between the peaks of the dark lobes 12 and 12′. The two lobes arephase shifted by 180 degrees.

Dark beams can be generated in such a way that they maintain asharply-defined energy distribution over a wider depth of field, thusoffering a better trade-off between size and concentration whenimplemented in scanning laser probe measuring technique or in TOT.Further, additional information, unavailable in a TOT, is available withthe dark beam, enabling more precise measurements. A few ways to realizethese forms could be considered and are covered in the references listedin the bibliography of U.S. Pat. No. 7,746,469; and those references arehereby incorporated by references in their entirety.

The optical setup described in U.S. Pat. No. 7,746,469 comprises asingle forward-looking detector. The particle size is measured for smallparticles by the depth of modulation of the dark line, and for largeparticles by the width of the interaction. The optical setup alsocomprises a scanner. The scanning speed is much higher than the particlevelocity, so the particle speed is assumed to be negligible; andtherefore, the particle size can be determined from the beam speed,interaction width and modulation depth of the interaction signal, andthe width of the beam.

The subject matter of patent application US 2015/0260628 (which ishereby incorporated by reference in its entirety), is a method andapparatus for particle size and concentration measuring that improves onthe method described in U.S. Pat. No. 7,746,469.

Reference is made to FIG. 2 , which is a schematic illustration of asystem. FIG. 2 schematically shows the measurement system described inUS 2015/0260628. The system shown in FIG. 2 comprises a laser 20, whichgenerates a Gaussian beam; spherical lenses 22 and 24, which togethercollimate the beam and act as a beam expander 26; phase mask 28, whichconverts the Gaussian laser beam into a structured dark beam with a linesingularity; a beam splitter 30 collecting the back scattered light; afocusing lens 32, which focuses the dark beam inside a cuvette 34through which liquid or air containing particles 36 flow in thedirection of the arrow Y; and two horizontal forward detectors 38 and 40(for clarity, rotated to the plane of the paper). It is noted that inthe case of airborne particles, the air stream bearing the particlesneed not necessarily be confined within a cuvette. Backscatter radiationfrom a particle 36 in the focus of the focusing lens 32 is collected bythe focusing lens 32, inherently collimated, reflected by beam splitter30, and directed via the collecting lens 42, which focuses the radiationthrough pinhole 44 onto a backscatter detector 46.

Reference is made to FIG. 3 , which is a schematic illustrationdemonstrating positioning of detectors. The positioning of the detectors38 and 40 with respect to the illuminating dark beam pattern is shown inFIG. 3 . In FIG. 3 , the Z-axis is the optical axis perpendicular to theplane of the paper; the Y-direction is the direction of particle flowperpendicular to the Z-direction in the plane of the paper; and theX-direction is perpendicular to Z also in the plane of the paper. Asshown in the figure, the two detectors are located in the X-Y plane atdifferent locations in the Y-direction parallel to the dark beam linesingularity symmetrically one on each side of the dark line 14; withdetector 38 positioned to cover partially intensity lobe 12; anddetector 40 positioned symmetrically to cover partially intensity lobe12′ of the dark beam. Referring to FIG. 3 , as particles cross the beamfrom top to bottom, the output intensity pattern is modified, and thedetectors sense a shift in the phase. Basically, the minute scatter froma small particle crossing one lobe interacts with the second lobe in ahomodyne mode. This yields higher sensitivity and additionalinformation, as the scattering is spatially separated before detection,rather than integrated.

The detectors spacing can be optimized or modified or configured forsensitivity, by aligning it to the maximum intensity gradient of thedark beam. For various analytic purposes, the detector signals can berecorded either: (a) as separate signals; (b) as a differential signalof the two detector signals; and (c) as the sum of the two detectorsignals. Subtracting the signals of the two detectors eliminates commonnoise, such as laser noise; and thereby improves the sensitivity of themeasurements over those made using the system of U.S. Pat. No.7,746,469.

The signal detected results from the phase difference and its sizedependency is typically r{circumflex over ( )}2.5.

The signal dependency of r{circumflex over ( )}2.5 is shown in thefollowing table, and in the graphs 1401 and 1402 on PSL (Poly StyreneLatex) beads of FIG. 14 .

Measurement Results

Vp-p PSL Concentration Average Diameter {circumflex over ( )} Flow RatePSL [nm] [#/ml] [mV] 2.5 250 sccm (Background) 0 26.48 — 250 sccm 225.127E+12 35.35 2270.2 250 sccm 29 2.687E+13 41.67 4528.9 250 sccm 463.606E+11 76.32 14351.4 250 sccm 70 2.509E+11 178.80 40996.3

The delay between the signals from the two forward detectors 38 and 40is used to derive information on the location along the optical axis Zat which the interaction with the particle took place; and, therefore,improves the accuracy; because if the location along the direction ofbeam propagation is known, then the corresponding beam profile at thatlocation is known and can yield higher accuracy in determining theparticle size based on the interaction signal, de-convolving the beamprofile. Alternatively, the delay can be used to reject particles thatdo not interact with the beam at the focus. In U.S. Pat. No. 7,746,469,rejection of measurements for particles that do not pass through thefocal point of the dark beam is based on the slope of the interactionsignal, which is less accurate. It requires knowledge of the relativevelocity of the particle. In patent application publication US2015/0260628, one can derive the velocity without any scanning, based onthe transit time between the two lobes on the two detectors (e.g., knowndistance between the lobes, divided by time between signals). Thistypically yields a lower noise and higher sensitivity than with ascanning beam.

Backscatter detector 46 detects the backscatter from the interaction ofthe particle with the dark beam through pinhole 44. Because of thepinhole 44, the detection is confocal and only particles that moveexactly in the focus of the dark beam will be detected by thebackscatter detector 46. The signals from the backscatter detectorprovide additional information including: additional information on theparticle size via intensity, width and modulation; reflection propertiesof the particle; fluorescence generated by the illuminating beam (givena suitable wavelength is chosen); and when combined with signals fromthe two forward detectors, may function as a high-resolutionone-dimensional confocal scanning microscope, and/or can revealinformation that is used to characterize specific particles and/or toclassify individual particles by clustering their nature of interaction.

Another improvement of the apparatus of US 2015/0260628 is that the useof two forward detectors in the system as described eliminates thenecessity of scanning, and the measurements can be carried out with astationary beam to measure the velocity of the particle as explainedabove. This is achieved by measuring the velocity of particles passingin the focal zone (delay=0 between the two detectors signals), where thegap between the lobes is known. This can easily be implemented whenparticles are small compared with that gap, but also for largerparticles, where the gap is shown as a graded signal ramp, with aplateau in the middle of the rise time and fall time.

One limitation of the methods described in U.S. Pat. No. 7,746,469 andUS 2015/0260628 is that the spot size of the illuminating beam is stillhighly focused, and therefore the rate of interaction with the particlesis low, and the methods are typically effective for relatively highparticle concentrations.

SUMMARY OF THE INVENTION

It is therefore a purpose of the present invention to outline a systemand method that provide accurate measurement of particle size andconcentration for low concentrations of contaminants in clear liquidsand gases, while maintaining the advantages of the techniques describedabove, and/or to facilitate size sensitivity down to the 20 nm range andbelow as needed in clean liquids and air in the Semiconductor andPharmaceutical industries. It is further a purpose of the presentinvention to outline and explain several configurations for improveddetection sensitivity down to 7 nm PSL and even below.

Further purposes and advantages of this invention will appear as thedescription proceeds.

The invention covers various aspects of enhancing the performance ofparticle detection based on interaction with a dark beam. Covered underthe invention are, for example: provisions and mechanisms for detectingin low concentration; provisions and mechanisms for determining ordetecting or estimating more information using several wavelengths;provisions and mechanisms for different beam profiles; provisions andmechanisms for improved sensitivity using dual and multi path detection;provisions and mechanisms for reducing noise via polarization, includingprovision and mechanism to create a delay between two polarizations orbetween two polarized components; provisions and mechanisms for moreinformation for clustering—back scatter, multi-color interaction;provisions and mechanisms for phase and amplitude separate analysis;and/or provisions and mechanisms for detection under low Signal to NoiseRatio (SNR) using pattern recognition.

In an aspect, provided is a particle detection system comprising: i) aflow cell for flowing a fluid containing particles; ii) an opticalsource for generating a beam of electromagnetic radiation; iii) a beamshaping optical system for receiving the beam of electromagneticradiation; the beam shaping optical system for generating an anamorphicbeam and directing at least a portion of the anamorphic beam through theflow cell; iv) at least one optical detector array in opticalcommunication with the flow cell and the optical source; wherein theoptical source directs the beam electromagnetic radiation to the opticallens thereby generating the anamorphic beam, wherein the portion of theanamorphic beam directed through the flow cell is provided to the atleast one optical detector array which measures an interaction betweenthe portion of the anamorphic beam and particles present in the flowcell, thereby generating a plurality of individual signals correspondingto elements of the at least one optical detector array; and v) ananalyzer for generating a differential signal from the individualsignals indicative of the particles.

The beam shaping optical system may comprise one or more cylindricallens. The at least one optical detector array may be positioned toreceive forward propagating electromagnetic radiation.

In an aspect, provided is a particle detection system comprising: a) aflow cell for flowing a fluid containing particles; b) an optical sourcefor generating a beam of electromagnetic radiation; c) an opticalsteering system in optical communication with the flow cell and theoptical source, for directing the beam through the flow cell at leasttwice; wherein the particles in the flow cell interact with differentportion of the beam on each individual pass through the flow cell; d) anoptical detection system for receiving electromagnetic radiation fromthe flow cell on to at least one optical detector array for generating aplurality of individual signals from the interactions with the beam; ande) an analyzer for generating a differential signal from the individualsignals indicative of the particles.

The optical steering system may direct the beam to pass through the flowcell at least four times, at least six times, or optionally, at leasteight times. The optical steering system may comprise a half wave plate,a quarter wave plate or both for altering a polarization state of thebeam.

The analyzer may analyze the differential signal in the time domain. Theanalyzer may count the particles base on the differential signal. Theanalyzer may characterize the size of the particles.

The beam of electromagnetic radiation may be a Gaussian beam, anon-Gaussian beam, a structured non-Gaussian beam, a dark beam, or astructured, dark beam. The anamorphic beam may be a top hat beam,Gaussian beam or a structured, dark beam.

The particle detection systems and methods described herein may furthercomprise at least one backscatter detector in optical communication withthe flow cell. the backscatter detector may detect reflectivity of theparticles. The backscatter detector may detect fluorescence of theparticles. The backscatter detector may be used to determine if theparticle is biological or non-biological.

The at least one optical detector array may be a segmented lineardetector array. The differential signal may be generated by particledetection system in analog.

The particle detection system and methods described herein may furthercomprise a processor. The differential signal may be generated by theprocessor. The processor may compare each output differential signalwith a pre-generated library of known signals corresponding to particlesto determine if each output signal corresponds to a particle detectionevent or laser noise. The processor may convert each output differentialsignal to the frequency domain using a Fourier transformation or a fastFourier transformation.

In an aspect, provided is a method for detecting particles comprising:i) providing at least one optical detector array in opticalcommunication with a flow cell; ii) generating one or more beams ofelectromagnetic radiation; iii) shaping the one or more beams ofelectromagnetic radiation using a beam shaping optical system togenerate an anamorphic beam and such that at least a portion of theanamorphic beam is directed through the flow cell and provided on to theat least one optical detector array; iv) flowing a fluid through theflow cell, thereby generating interactions between the anamorphic beamand the particles present in the fluid; v) detecting interactions withthe particles and the anamorphic beam in the flow cell using the atleast one optical detector array, thereby generating detector outputsignals corresponding to elements of the at least one optical detectorarray; vi) generating a differential signal based on two or more of thedetector output signals; and vii) analyzing the differential signal todetect and/or determine one or more characteristics of the particles.

In an aspect, provided is a method for detecting particles comprising:i) providing at least one optical detector array and a flow cell forflowing particles; ii) generating at least one beam of electromagneticradiation and directing the beam to an optical steering system; iii)directing the beam using the optical steering system such that the beampasses through the flow cell at least twice; iv) flowing a fluid throughthe flow cell, thereby generating interactions between the beam and theparticles in the fluid, wherein interactions between the particles andthe beam occur in a different portion of the beam on each individualpass; v) directing the beam on to at least one optical detector arrayfor generating a plurality of detector signals from the interactionsbetween the particles and the beam; vi) generating a differential signalbased on the plurality of detector signals; vii) analyzing thedifferential signal to detect and/or determine one or morecharacteristic of the particles.

The step of analyzing the differential signals may be performed in thetime domain. The beam of electromagnetic radiation may be a Gaussianbeam, a non-Gaussian beam, a structured non-Gaussian beam, a dark beam,or a structured, dark beam. The anamorphic beam may be a top hat beam,Gaussian beam or a structured, dark beam.

The beam shaping optical system may comprise one or more cylindricallens. The at least one optical detector arrays may be a segmented lineardetector array.

The step of analyzing the differential signal may include comparing thedifferential signal with a pre-generated library of known signalscorresponding to particles and determines if the differential signalcorresponds to a particle detection event or laser noise. The step ofanalyzing the differential signal may include converting thedifferential signal into the frequency domain using a Fourier transformor a fast Fourier Transform. The step of analyzing the differentialsignal may include characterizing the particles, for example, countingthe particles, determining the size of the particles, or both.

Additionally, the additional embodiments and systems described hereinmay be usefully incorporated in the described methods.

“Anamorphic beam,” as used herein, refers to a beam of electromagneticradiation characterized by independent optical power in more than onespatial dimension. An anamorphic beam may have different optical powerin more than one spatial dimension. An anamorphic beam may haveindependent and different optical power in two spatial dimensionscorresponding to the cross-sectional area of the flow cell (e.g. the x-yplane which the particles pass through if flowing in the z direction).

“Optical detector array” refers to a group or array of individualdetector elements, for example, a one-dimensional or two-dimensionalarray of photodetectors or photodiodes.

All the above and other characteristics and advantages of the inventionwill be further understood through the following illustrative andnon-limitative description of embodiments thereof, with reference to theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows two-dimensional intensity profiles of a Gaussian beam and adark beam.

FIG. 2 schematically shows a prior art particle monitoring system.

FIG. 3 schematically shows the positions in the detector plane of theforward detectors of the system of FIG. 2 with respect to theilluminating dark beam pattern.

FIG. 4 schematically shows an embodiment of the particle monitoringsystem of the present invention, where the focal zone is elongated and acollecting optics projects the lobes on the detector array, that is thenconnected to a DAQ (Data Acquisition board or sub-system).

FIG. 5 shows schematically the two lobes of the beam at the detectionplane which is partially covered by a dual detector array, in accordancewith the present invention, and wherein in the array, each pairfunctions as detectors 38 and 40 of FIG. 3 .

FIG. 6 schematically shows an embodiment of an optical setup fordetecting and measuring the size and concentration of small particles onthe surface of a wafer or on other surface, in accordance with thepresent invention.

FIG. 7 schematically shows the scanning direction used with the opticalsetup of FIG. 6 , in accordance with the present invention.

FIGS. 8A, 8B and 8C schematically illustrate the collecting optics witha line focus, having Fourier Transform (FT) in Y direction and imagingin the X direction, in accordance with the present invention.

FIG. 9 is a schematic illustration of a system implementing a modifiedsetup based on the method of US 2015/0260628 with two wavelengths, orwith a plurality of wavelengths, in accordance with the presentinvention.

FIG. 10 shows schematically the Single-path detection scheme and theimproved Dual-path and Multi-path detection schemes, in accordance withthe present invention.

FIG. 11 shows a labeled photograph of an exemplary implementation of anembodiment of the Dual Path system, in accordance with the presentinvention.

FIG. 12 shows schematically a Fluorescent detection scheme, inaccordance with the present invention.

FIG. 13 shows schematically an approach to further enhance the SNR viapolarization, in accordance with the present invention.

FIG. 14 shows schematic illustrations of two graphs demonstrating signaldependency, in accordance with the present invention.

FIG. 15 demonstrates an example of the interaction detected on onechannel, in accordance with the present invention.

FIG. 16 demonstrates an example of a differential signal, demonstratingthe difference between top and bottom PDA elements, in accordance withthe present invention.

FIG. 17 demonstrates matching pattern shapes as detected by an algorithmin accordance with the present invention.

FIG. 18 demonstrates filter parameters in accordance with the presentinvention.

FIG. 19 demonstrates an interaction scattering plot, generated inaccordance with the present invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

In order to improve sensitivity of the measurements for lowconcentrations of contaminants in clear liquids or gases, the inventorshave modified the optical system of FIG. 2 by inter alia changing lens32 from a spherical to a cylindrical lens. The optical energydistribution in the present invention, an embodiment of which isschematically shown in FIG. 5 , comprises a line focus with a dark linesingularity. Other optical designs to achieve a higher level ofanamorphic beam profile are part of the present invention, including tophat line distribution in X direction. The focused beam interacts withparticles, same as explained above for a circular focus, and thenprojected on to a detector array and thus achieves parallel detection bymultiple detector pairs in the form illustrated and explained above onFIG. 3 . An additional cylindrical collecting optics, shownschematically in FIG. 4 , could be used between the focal zone and thedetector to match the beam profile to the detector size. The lens can beused, for example, to create imaging in X direction and FourierTransform in the Y direction. An example of such a lens design is shownschematically in FIG. 8A; further showing in FIG. 8B the imaging in Xdirection on a detector of 4 mm; and further showing in FIG. 8C theFourier Transform in the Y direction.

As a result of this, if, as in FIG. 2 , in FIG. 4 the Z-axis is theoptical axis in the plane of the paper, the Y-axis is the direction ofparticle flow perpendicular to the Z-direction also in the plane of thepaper, and the X-direction is perpendicular to the plane of the paper,then the focus of the illuminating beam at the location of theinteraction with the particles is very sharp in the Y-direction and arelatively very elongated line in the X-direction ideally with a top hatdistribution [Optical design to achieve flat energy distribution in apreferred direction] along the X direction, which is the direction ofthe dark line singularity. Illustrative but not limiting dimensions forthe focus that were used in a system built and tested by the inventorsare: 1 micron dark beam in the Y-direction, and 120 microns top hat inthe X-direction. In the specific embodiment of the system that has beenbuilt and used by the inventors to test the method, the detector arraycomprised 32 pairs of Si PIN photodiode detector elements. Thus, for theforward detectors, each pair of elements imaged 120/32≈4 microns.

In the X-direction, the detector sees an image of the beam and, for theexemplary embodiment described above in which the detector array is 4 mmlong, the 120 micron width of the focal zone is magnified to 4 mm. Inthe Y-direction, the forward scatter detectors of FIG. 3 , or the backdetectors of FIG. 6 (see herein below), see the Fourier transform (FarField) of the beam.

It is possible to extend the focus in this way in the direction withoutaffecting the spatial resolution in the Y direction, because theparticles are flowing in the Y-direction and therefore interact withonly the narrow side of the beam.

There is a significant challenge of SNR and contrast when trying todetect a 10-20 nanometer particles in a 120×1 micron² focal area, evenbased on the singularity and homodyne approach mentioned in U.S. Pat.No. 7,746,469 and US 2015/0260628. To overcome this problem in thepresent invention, the two forward horizontal detectors 38 and 40 shownin FIG. 2 are replaced by two segmented matched linear arrays ofdetectors 38* and 40* in the system shown in FIG. 5 .

FIG. 5 symbolically shows the position of the detector arrays 38* and40* relative to the dark line 14 and peak intensity regions of the twolobes 12 and 12′ of a dark beam in the detector plane. The measurementsare carried out using signals from corresponding pairs of detectorelements across the dark line (for example, 1 a and 1 b in FIG. 5 ).This way, parallel detection is facilitated on the pairs in the array,while maintaining the same spatial resolution; and, as long as the laserpower density in the focal zone is the similar to the one in FIG. 2 ,the same SNR is achieved. The rate of interaction of the focused beam isthus increased typically by a factor equivalent to the number ofdetector pairs.

The backscatter detector 46 shown in FIG. 2 , in the case of the newinvention, can be extended to a detector 46*, which can be either asingle detector such as backscatter detector 46 in the prior art system,but it is advantageous to use two detectors 46*a and 46*b in order to beable to measure the differential signals and thereby reduce the effectof random noise. In this embodiment of the system, the two detectors46*a and 46*b that may be incorporated into a system such as that ofFIG. 2 , can be either just a single detector or dual detector, of highsensitivity detector such as a PMT or APD, covering the image of theline focus. The back scatter is in dark field, hence there is typicallyno need for an array of detectors to reduce the background shot noise.Still, segmented linear arrays similar to forward detectors 38* and 40*can be considered for other benefits, such as a continuous area or flowmapping with high sensitivity, and/or for improved detection rate andclustering as with the forward detector array.

FIG. 6 shows a special embodiment where the particles are on the surfaceof a Si wafer. The wafer is reflective, and hence the detector array 58is position-wise equivalent to the forward scatter where the beam isreflected back, passing twice through the particle. The detector array58 in this configuration measures the sum of the forward scatteringreflected from the wafer, after passing twice through the particle, andthe backscatter. Using a line focus and segmented linear array detectorsto measure the backwards beam, as mentioned above, is especially usefulfor low concentrations of particles, as the coverage area with a linefocus is bigger. Typically, a whole wafer coverage to detect 10 nmparticles or smaller, can be accomplished in a few minutes, complyingwith the rate of 10-20 wafers per hour, while achieving superiorresolution. An example of an embodiment is a top hat width of 0.5 mm anda scanning speed of the wafer relative to the beam of 1 m/sec. Thisyields a detection area of 500 mm{circumflex over ( )}2/sec; and for a300 mm wafer, a full coverage would be in less than 3 minutes.

DAQ:

In order to handle the output from the detectors, a dedicated dataacquisition system (DAQ) and algorithms were developed by the inventors.The output of each photodiode is fed into one of the 64 input channelsof the DAQ, which comprises inter alia a low noise preamplifier,components to provide a triggered output, buffers, and an interfaceboard between the two detectors in each pair to allow for multiplexingof the output signals or transferring of distinct events.

In one embodiment, for example, the DAQ system comprises four boards,and utilizes algorithms of smart sequencing of the detector elements andtheir connections to the DAQ, where detectors 1, 2, 3, 4 are channeledto different acquisition boards, and then channels 5, 6, 7, 8 arechanneled to the same acquisition boards. Typically, the thresholding isdone in the DAQ, and only packets of configurable duration before andafter the threshold triggered event are transferred to a computer orprocessor for further processing. Each packet is accompanied by anaccurate time-stamp, so the concentration of events can be calculatedbased on the number of interaction and the known zone/volume ofinteraction. This approach is beneficial in low concentration, whererarely more than one of 4 adjacent detector pairs will encounterinteraction. This topology of the DAQ is such that, for example, if alarge particle passes a detector and causes a signal to be generated byup to four adjacent pairs of detector elements, the data acquisition issplit so that the signal from the 1st pair of elements goes to channel1, the signal from the 2nd pair goes to channel 2, the signal from the3rd pair goes to channel 3, the signal from the 4th pair goes to channel4, the signal from the 5th pair again goes to channel 1, the signal fromthe 6th pair again goes to channel 2, etc. In this way, information canbe gathered on larger particles whose interaction is recorded in severalchannels with close time-stamps.

The data transferred to an external processor or computer for furtherprocessing is efficient and includes only interaction information. Themajority of the time in low concentration, there will be no interaction,and no data will pass the threshold to be transferred to the processor.The concentration limit is so that two particles either cannotstatistically pass in front of the detectors at the same time, or thatthe algorithm is able to detect this and ignore measurements of all butsingle particle detections.

In cases of higher concentration, the strategy is to transfer all thedata to the external processor for analysis, as most of the time therewill be interaction signals. An embodiment related to detection in highconcentration is of a differential pre-amplifier subtracting between thetwo detectors in each pair. This embodiment allows initial thresholdingof the interaction signals. This is relevant, for example, in case thelarge tail of the particles is to be detected, such as in CMPapplications (Chemical Mechanical Polishing slurries). In this case, theinteractions can be optically filtered by the interaction intensity, toeliminate huge amount of small particles interactions.

Another advantage of the differential signal is the rejection of commonnoise, allowing even lower thresholding level and hence improving thesensitivity to small particles.

Of course, all the DAQ advanced capabilities mentioned above, areapplicable on the differential signal, allowing further processing.

The signal identification algorithm can determine particle size, type,and concentration. A description of the algorithm is as follows:

Pattern Matching for Low SNR:

FIG. 15 demonstrates an example 1501 of the interaction detected on oneof the channels.

One can see that Positive and Negative channels (Positive and Negativechannels are the reads from the two detectors in a single pair at thePDA) have certain relative structure.

FIG. 16 demonstrates an example 1601 of the differential signal, whichis their difference; for example, demonstrating the difference betweenthe top and bottom PDA elements.

The differential signal is less noisy than the two detected channels(Positive and Negative). In order to detect similar signal in lower SNRconditions, the inventors used pattern recognition based on matchedfilters and performed a convolution of the differential signal againstbank of filters:

y _(k)(t)=x(t)*h _(k)(t)

where x(t) is a differential signal; hk(t) is a specific matchingfilter; and yk(t) is an output. All filters hk(t) are normalized to unitenergy.

Since the shape of the signal x(t) depends on the beam structure,particle size and interaction location in XYZ space relative to thefocus, we create large number of matching filters hk(t), that can bereplaced in the future in case of different interactions.

In order to detect different signals, variable delay and width ofmatching filters is used, as demonstrated in example 1701 of FIG. 17 ,demonstrating matching pattern shapes in the algorithm.

Actually, the filter bank serves a non-orthogonal basis, which spanssignal subspace. The main ideas are outlined in papers related to sparsesignal representations. A relevant review is the publication by AlfredM. Bruckstein, David L. Donoho, Michael Elad: “From Sparse Solutions ofSystems of Equations to Sparse Modeling of Signals and Images”, SIAMReview (2009)—Society for Industrial and Applied Mathematics, Volume 51,Number 1, pages 34-81, which is hereby incorporated by reference in itsentirety.

The invention may represent each sensor response by the derivative ofthe Gaussian function, such as:

${f_{\sigma,m}(t)} = {{\frac{d}{dt}e^{- {(\frac{t - m}{\sigma})}^{2}}} \cong {{- 2}( \frac{t - m}{\sigma} )e^{- {(\frac{t - m}{\sigma})}^{2}}}}$

where amplitude values are ignored.

Since there are two lobes interacting with each other, the total filterresponse h(t) is:

${h_{\sigma,m}(t)} = {{{f_{\sigma,m}(t)} - {f_{{- \sigma},m}(t)}} \cong {{{- ( \frac{t - m}{\sigma} )}e^{- {(\frac{t - m}{\sigma})}^{2}}} + {( \frac{t + m}{\sigma} )e^{- {(\frac{t + m}{\sigma})}^{2}}}}}$

where it is assumed that the lobes are symmetric around zero and theirmean response are fm(t) and f−m(t).

Since the interaction can happen in any place on the Z axis, thealgorithm copes with different m and σ, which are called delay and widthparameters respectively. In order to detect from unknown Z distance, aset of filters hk(t) is generated; where k describes a certain pair {mk,σk}. Each filter is designed with certain delay and width parameter forPositive and Negative data channels as explained and demonstrated inexample 1801 of FIG. 18 , demonstrating filter parameters.

The absolute value of each output signal yk(t) is computed, and themaximal is compared with threshold (e.g., can be set by the Analysissoftware). The parameters of the filter that created maximal responseabove the threshold are used as indicators for delay and width.Amplitude is taken from the maximal yk(t).

Based on best matching filter parameters for all interactions, ahistogram is computed or generated; such as, example 1901 of FIG. 19 ,demonstrating an interaction scattering plot.

The method of the invention is suitable for measuring airborne andliquid-borne samples, and has been successfully tested by the inventorsfor both cases. An experimental setup used electro spray to generatenano particles. Results were as described in the following table:

Flow Rate PSL [nm] Vp-p Average [mV] 1500 sccm 20 (N/A, hard to get)1500 sccm 46 163.6667 1500 sccm 80 356.3333 1500 sccm 100 582.6667

Some examples of applications in which the method of the presentinvention can be used are: to monitor the quality of ultra-pure water orother liquids in the pharmaceutical and semiconductor industries, andthe environment air in a clean room. It is noted that in the case ofairborne particles, the air stream carrying the particles can be (butneed not necessarily be) confined within a cuvette, and the particlesvelocity can be determined by intrinsic interaction information, asexplained above.

In addition to measurements of airborne and liquid-borne particles, thesystem and method of the present invention can be used to detect andmeasure size and concentration of small particles on surfaces. Anillustrative example of an application of the method to suchmeasurements can be found in the semiconductor industry, where it isextremely important to detect and identify the presence, concentration,and size of dust and other microscopic particles on the surfaces of barewafers to be used as substrates in fabrication processes, or onreticles.

FIG. 6 schematically shows an embodiment of an optical setup fordetecting and measuring the size and concentration of small particles onthe surface of a wafer 54. Light emitted by laser 20 passes through beamisolator 48, focusing optics 50 with or without a provision to generatethe dark line singularity, and beam splitter 52 to wafer 54. The lightreflected from the surface of wafer 54 is split by the beam splitter 52into two portions. The first portion passes through focusing lens 50,and is absorbed by beam isolator 48. The second portion of the reflectedlight passes through collecting optics 56, and is detected by forwardlooking segmented linear detector array 58. The light signal from thedetector is comprised of the reflected forward scatter and thebackscatter, as explained above. FIG. 6 shows only the elementsnecessary to illustrate this application of the method. Not shown arethe optical elements used to form the dark beam or the linear focus.Detector array 58 comprises two detector arrays (Dual Array), forexample, as in FIG. 4 and FIG. 5 .

FIG. 7 schematically shows the scanning direction used with the opticalsetup of FIG. 6 . The Z-axis is the incoming optical axis; the X-axis isthe dark beam direction; the Y-axis is the scanning direction. The wafer54 is located on an X-Y scanning stage. An optional Tip Tilt Z stage canbe used, to assure that the imaged section of the wafer is in focus. Themethodology and the focus feedback sensor may be implemented based oncommon practices as known in the motion industry.

During a scan, the wafer 54 is moved in the Y direction, so thateffectively the (stationary) dark beam 60 moves over the surface ofwafer 54 in the direction of the arrow. To cover the entire surface ofthe wafer, Raster, Meander, or other scanning pattern can be applied. Infact, as the position of the array is known via the close loop controlof the scanning stage, an image or map of the contaminations can becreated.

The methods described in U.S. Pat. No. 7,746,469, in US 2015/0260628,and in the present patent application, can be carried out with manymodifications and improvements; such as those described as follows.

(1) Use of Other Beam Profiles:

Although the method has been described using a dark beam to interactwith the particles, it can be carried out using the same optical setupmutatis mutandis with other non-Gaussian structured beams or with aGaussian beam. When using a dark beam, the background signal is lower,and correspondingly the background shot noise is lower; however, thespot size for a Gaussian beam is smaller for a given numerical aperture,and therefore the interaction signal could be higher in someconfigurations. Thus, in some cases, the Gaussian beam can yield abetter signal-to-noise ratio (SNR).

Investigation has shown that Dark Beam becomes very effective with anoptimal photodiode detector, power and spot size. Dark Beam must besized such that the detector receives 50% of each lobe of the beam. Inorder to benefit from the Dark Beam, the signal must be strong enough(irradiance) to not be limited by detector noise/DAQ resolution.Divergence of the beam requires more laser power.

Analysis of Gold vs. PSL, and Dark Beam vs. Gaussian Beam:

Gold vs. PSL: the data suggests that the signal created by the PSL ismostly due to a phase enhancement, while the signal that is created bythe gold has also a strong component of obscuration.

Experimenting Dark Beam vs. Gaussian Beam: the interaction signal withthe Dark Beam is stronger by 2.66 compared with the interaction with theGaussian Beam.

(2) Use of Multiple Wavelengths:

Instead of using one illuminating laser as described above, anembodiment of the optical system comprises two or more illuminatinglasers, each one having a different wavelength. They all have the samefocal zone, and share some of their measurement cross-section.Therefore, by rapidly switching between them, and by synchronizing thedetection to the switching rate, it is possible not only to detect whena nanoparticle passes through the beam, but also to better characterizewhat type of particle it is, based on the additional spectralinformation.

Another embodiment of this multi wavelength method and system uses adichroic beam splitter and two detectors, so switching between thelasers is not required, getting both wavelength signals in parallel.Expanding our Dark Beam measuring method, to two Dark beams, withdifferent wavelengths (λ1, λ2), that are directed along the same opticalpath and focused to the cuvette center, as shown in system 901 of FIG. 9.

In the case of an objective with a chromatic aberration, we increase thecross section of detection, because each wavelength has a differentfocal zone along the optical axis.

In the case of achromatic objective, it is possible to think about theParticle-Beam interaction as two separate interactions for the sameparticle. Each interaction explores the particle's refractive index witha different wavelength, and improves the SNR and the ability tocharacterize the particles based on their spectral behavior.

(3) Use of Polarization:

In other embodiments of the present invention, polarizing opticalelements are included to enable enhanced performance of the system andinvestigation of properties of the particles that are revealed bypolarized light.

The detection via crossed polarizers allows a birefringent signal fromthe particle to be detected while reducing the background noise.

(4) Use of Dual Path/Multiple Path Detection Scheme:

Another embodiment of the present invention is of dual path or multiplepath (multi-path) of the beam through the particle, thus improving thesignal level. The same beam is re-directed again to interact with thesame particle in the cuvette, and by that increases the SNR.

This is shown in FIG. 10 , which demonstrates a single-path setup 1001,a double-path (or dual-path) setup 1002, and a multi-path (ormultiple-path) setup 1003, in accordance with some embodiments of thepresent invention.

In the embodiments shown in FIG. 10 , for example: numeral 1 indicatesthe laser (e.g., laser transmitter, laser generator, laser beam source);numeral 2 indicates an isolator; numeral 3 indicates a beam expander;numeral 4 indicates a mirror; numeral 5 indicates a phase mask; numeral6 indicates a half-wave plate; numeral 7 indicates a mirror; numeral 8indicates an objective; numeral 9 indicates a cuvette; numeral 10indicates a collecting optics element; numeral 11 indicates a detector;numeral 12 indicates a polarized beam splitter; numeral 13 indicates amirror; numeral 14 indicates a quarter-wave plate; numeral 15 indicatesa semi-transparent mirror.

The explanation for the improvement among single-path, dual-path, andmulti-path, is as follows.

Scattering Calculation:

For very small particles compared with the beam diameter, the signalincreases each time the beam interacts with the particle.

${signal} = {{{2{ttS}} + {2{ttSr}} + {2{ttSrr}} + \ldots} = \frac{2{St}^{2}}{1 - r}}$

Where: t is the transmission parameter of the mirror; r is thereflectance; S is the signal.For a semi-transparent mirror, we can claim:

t ² +r ²=1

Therefore, we can write:

signal=2S(1+r)

It can be shown that both the forward and the back scattering can berepresented by 1, so one can write:

S=S(Forward Scatter)+S(Back Scatter)

For small particles, forward and the back scattering have similaramplitude, so by choosing r→1, up to 8 times better SNR can be achieved,in some embodiments.

Another explanation relates to the generation of standing waves as aresult of the interaction of the propagating and reflected beam. Thiscreates peaks and zeros of the energy along the optical axis. The peakenergy is higher and provides higher power density and higher SNR. Thepeak is narrow along the optical axis Z, but this can be wellcompensated by extending the beam in the X direction,

A labeled photograph of a representative implementation of a Dual Pathsetup, in accordance with the present invention, is shown in FIG. 11 .

(5) Fluorescence Detection:

Another embodiment of the present invention allows for fluorescentdetection. The concept and setup are demonstrated in system 1201 of FIG.12 , in accordance with the present invention.

By using a short wavelength, such as 405 nm illumination for laser L,fluorescence is generated from living organisms; and the additionaldetection here will allow better clustering and separation betweeninorganic and organic substances, functioning as a high spatialresolution flow cytometer.

(6) Polarization, Delay and Interferometric Detection:

In an interferometric detection technique, presented above, the signaldrops as (approximately as) the third power of the particle size,whereas the scattering signal drops as the sixth power. SNR can beimproved significantly by analyzing dark field rather than bright filed.Further, phase and amplitude can be analyzed separately by aligning theanalyzer.

Another embodiment is described herein. In the Dark-Beam (DB) Dual-PassCommon-path Interferometer system, the incoming beam (pump) passesthrough a calcite and splits to two beams, parallel and perpendicularpolarized beams with a short delay in time. The perpendicular polarizedbeam (leading beam) interacts with the particle, but the other does not.They are recombined by a second crystal, and their interference ismonitored on (or by) the detector (dark-field).

FIG. 13 shows schematically an approach to further enhance the SNR viapolarization, in accordance with the present invention. System 1301 ofFIG. 13 demonstrates polarization enhancement to the dual-path ormultiple-path detection scheme, in accordance with the presentinvention.

In FIG. 13 , for example: numeral 1 indicates a laser; numeral 2indicates an isolator; numeral 3 indicates a beam expander; numeral 4indicates a mirror; numeral 5 indicates a phase mask; numeral 6indicates a half-wave plate; numeral 7 indicates a mirror; numeral 8indicates a BS-polarizer (e.g., a beam-splitter polarizer, or apolarizing beam-splitter, or a combined beam-splitter and polarizer);numeral 9 indicates a quarter-wave plate; numeral 10 indicates apolarizer; numeral 11 indicates a detector; numeral 12 indicates aquarter-wave plate; numeral 13 indicates a polarizer; numeral 14indicates a calcite or a calcite crystal; numeral 15 indicates anobjective; numeral 16 indicates a cuvette; numeral 17 indicates acollecting optics; numeral 18 indicates a calcite or a calcite crystal;numeral 19 indicates a mirror.

As demonstrated in FIG. 13 , in the Dark-Beam Dual-Pass Common-pathInterferometer, a 45-degrees polarized beam from vertical is passedthrough a calcite, and splits into two orthogonally polarized beams witha short delay in time (Δt). The perpendicular polarized beam, which isdefined by the fast-optical axis of the calcite, travels in front. Attime t, the single nanoparticle will interact with the beam, having aphase-shift between two polarizations. Both beams are recombined by asecond calcite, and their interference is monitored on the detector.

Due to dark-field operation of this interferometry, the resolution ofdetection is photon-noise limited. Also, since the amplitude and phaseresponse of the scattered field are separated in this system, thus, onecan extract information hidden in phase (scattering) and amplitude(absorption). This can be done by only adjusting the angles betweenpolarizer and quarter-wave plate.

This interferometry is operated on Homodyne mode, but can also beoperated at reflection mode (Heterodyne mode). In that case, only onecalcite crystal is needed.

Some embodiments of the present invention include an optical system forparticle size and concentration analysis, the optical system comprising:(a) at least one laser that produces an illuminating beam; (b) afocusing lens that focuses said illuminating beam on particles that moverelative to the illuminating beam at known angles to the illuminatingbeam through the focal region of the focusing lens; (c) at least twoforward-looking detectors, that detect interactions of particles withthe illuminating beam in the focal region of the focusing lens; whereinthe focusing lens is a cylindrical lens that forms a focal region thatis: (i) narrow in the direction of relative motion between the particlesand the illuminating beam, and (ii) wide in a direction perpendicular toa plane defined by an optical axis of the system and the direction ofrelative motion between the particles and the illuminating beam; whereineach of the two forward-looking detectors is comprised of two segmentedlinear arrays of detectors.

In some embodiments, the system is configured to operate on reflectionfrom a surface to detect particles on the surface.

In some embodiments, the system is configured to operate on reflectionfrom a wafer surface to detect particles on the wafer surface.

In some embodiments, the system further comprises: a back-scatterdetector to perform back-scatter detection and/or for focusdetermination of the particle pathing through a cuvette.

In some embodiments, the system further comprises: a back-scatterdetector to perform color analysis of the particle.

In some embodiments, the system further comprises: a back-scatterdetector to perform fluorescence detection enabling to differentiatebetween organic particles and inorganic particles.

In some embodiments, the system further comprises: dichroic mirror todetect both back-scatter and fluorescence.

In some embodiments, the system further comprises: a particle velocitymeasurement unit, to determine particle velocity based on the time offlight of the particle through two peaks of a Dark Beam.

In some embodiments, the system is configured to operate in a Dual Pathmode which enhances the detection via super-position of two interactionsof the particle with the propagating beam and the reflected beam.

In some embodiments, two mirrors create a resonator which enablesmultiple paths of the signal and thereby an enhanced signal.

In some embodiments, the system utilizes crossed-polarization (i) toeliminate the laser background signal, and (ii) to benefit frombirefringence of particles, and (iii) to enable dark field detection.

In some embodiments, the system further comprises: a data acquisitionssub-system for a dual array with periodicity in detection, to enabledetection of small and large particles.

In some embodiments, the system further comprises: a pattern matchingunit, to perform pattern matching of (i) an array of syntheticallygenerated potential interactions, with (ii) the actual interaction, andto enable particle detection at lower SNR ratio by utilizing patternmatching.

In some embodiments, the system utilizes a Dark Beam.

In some embodiments, the system utilizes a Gaussian Beam.

In some embodiments, the system utilizes both a Dark Beam and a GaussianBeam.

In some embodiments, the system utilizes multiple different wavelengths.

In some embodiments, the system utilizes multiple different wavelengthswith a chromatic objective to enhance the interaction volume.

In some embodiments, the system utilizes multiple different wavelengthswith an achromatic objective to derive more information on theparticles.

In some embodiments, the system is configured as a Dual Path setup whichcomprises a Dual Path in the Dark-Beam (DB) and a common-pathInterferometer; wherein an incoming beam (pump) is passed through acalcite, and splits to two beams, which are parallel and perpendicularpolarized beams with a short delay in time; wherein the perpendicularpolarized beam (leading beam) interacts with the particle; wherein theparallel polarized beam does not interact with the particle; wherein thetwo beams are recombined by a second crystal, and wherein theirinterference is monitored on the detector (dark-field layout).

The system(s) of the present invention may optionally comprise, or maybe implemented by utilizing suitable hardware components and/or softwarecomponents; for example, processors, processor cores, Central ProcessingUnits (CPUs), Digital Signal Processors (DSPs), GPUs, circuits,Integrated Circuits (ICs), controllers, memory units, registers,accumulators, storage units, input units (e.g., touch-screen, keyboard,keypad, stylus, mouse, touchpad, joystick, trackball, microphones),output units (e.g., screen, touch-screen, monitor, display unit, audiospeakers), acoustic sensor(s), optical sensor(s), wired or wirelessmodems or transceivers or transmitters or receivers, GPS receiver or GPSelement or other location-based or location-determining unit or system,network elements (e.g., routers, switches, hubs, antennas), and/or othersuitable components and/or modules. The system(s) of the presentinvention may optionally be implemented by utilizing co-locatedcomponents, remote components or modules, “cloud computing” servers ordevices or storage, client/server architecture, peer-to-peerarchitecture, distributed architecture, and/or other suitablearchitectures or system topologies or network topologies.

In accordance with embodiments of the present invention, calculations,operations and/or determinations may be performed locally within asingle device, or may be performed by or across multiple devices, or maybe performed partially locally and partially remotely (e.g., at a remoteserver) by optionally utilizing a communication channel to exchange rawdata and/or processed data and/or processing results.

Although portions of the discussion herein relate, for demonstrativepurposes, to wired links and/or wired communications, some embodimentsare not limited in this regard, but rather, may utilize wiredcommunication and/or wireless communication; may include one or morewired and/or wireless links; may utilize one or more components of wiredcommunication and/or wireless communication; and/or may utilize one ormore methods or protocols or standards of wireless communication.

Some embodiments may be implemented by using a special-purpose machineor a specific-purpose device that is not a generic computer, or by usinga non-generic computer or a non-general computer or machine. Such systemor device may utilize or may comprise one or more components or units ormodules that are not part of a “generic computer” and that are not partof a “general purpose computer”, for example, cellular transceivers,cellular transmitter, cellular receiver, GPS unit, Graphics ProcessingUnit (GPU), location-determining unit, accelerometer(s), gyroscope(s),device-orientation detectors or sensors, device-positioning detectors orsensors, or the like.

Some embodiments may be implemented as, or by utilizing, an automatedmethod or automated process, or a machine-implemented method or process,or as a semi-automated or partially-automated method or process, or as aset of steps or operations which may be executed or performed by acomputer or machine or system or other device.

Some embodiments may be implemented by using code or program code ormachine-readable instructions or machine-readable code, which may bestored on a non-transitory storage medium or non-transitory storagearticle (e.g., a CD-ROM, a DVD-ROM, a physical memory unit, a physicalstorage unit), such that the program or code or instructions, whenexecuted by a processor or a machine or a computer, cause such processoror machine or computer to perform a method or process as describedherein. Such code or instructions may be or may comprise, for example,one or more of: software, a software module, an application, a program,a subroutine, instructions, an instruction set, computing code, words,values, symbols, strings, variables, source code, compiled code,interpreted code, executable code, static code, dynamic code; including(but not limited to) code or instructions in high-level programminglanguage, low-level programming language, object-oriented programminglanguage, visual programming language, compiled programming language,interpreted programming language, C, C++, C#, Java, JavaScript, SQL,Ruby on Rails, Go, Cobol, Fortran, ActionScript, AJAX, XML, JSON, Lisp,Eiffel, Verilog, Hardware Description Language (HDL, BASIC, VisualBASIC, Matlab, Pascal, HTML, HTML5, CSS, Perl, Python, PHP, machinelanguage, machine code, assembly language, or the like.

Discussions herein utilizing terms such as, for example, “processing”,“computing”, “calculating”, “determining”, “establishing”, “analyzing”,“checking”, “detecting”, “measuring”, or the like, may refer tooperation(s) and/or process(es) of a processor, a computer, a computingplatform, a computing system, or other electronic device or computingdevice, that may automatically and/or autonomously manipulate and/ortransform data represented as physical (e.g., electronic) quantitieswithin registers and/or accumulators and/or memory units and/or storageunits into other data or that may perform other suitable operations.

The terms “plurality” and “a plurality”, as used herein, include, forexample, “multiple” or “two or more”. For example, “a plurality ofitems” includes two or more items.

References to “one embodiment”, “an embodiment”, “demonstrativeembodiment”, “various embodiments”, “some embodiments”, and/or similarterms, may indicate that the embodiment(s) so described may optionallyinclude a particular feature, structure, or characteristic, but notevery embodiment necessarily includes the particular feature, structure,or characteristic. Furthermore, repeated use of the phrase “in oneembodiment” does not necessarily refer to the same embodiment, althoughit may. Similarly, repeated use of the phrase “in some embodiments” doesnot necessarily refer to the same set or group of embodiments, althoughit may.

As used herein, and unless otherwise specified, the utilization ofordinal adjectives such as “first”, “second”, “third”, “fourth”, and soforth, to describe an item or an object, merely indicates that differentinstances of such like items or objects are being referred to; and doesnot intend to imply as if the items or objects so described must be in aparticular given sequence, either temporally, spatially, in ranking, orin any other ordering manner.

Some embodiments may be used in conjunction with one way and/or two-wayradio communication systems, cellular radio-telephone communicationsystems, a mobile phone, a cellular telephone, a wireless telephone, aPersonal Communication Systems (PCS) device, a PDA or handheld devicewhich incorporates wireless communication capabilities, a mobile orportable Global Positioning System (GPS) device, a device whichincorporates a GPS receiver or transceiver or chip, a device whichincorporates an RFID element or chip, a Multiple Input Multiple Output(MIMO) transceiver or device, a Single Input Multiple Output (SIMO)transceiver or device, a Multiple Input Single Output (MISO) transceiveror device, a device having one or more internal antennas and/or externalantennas, Digital Video Broadcast (DVB) devices or systems,multi-standard radio devices or systems, a wired or wireless handhelddevice, e.g., a Smartphone, a Wireless Application Protocol (WAP)device, or the like.

Some embodiments may comprise, or may be implemented by using, an “app”or application which may be downloaded or obtained from an “app store”or “applications store”, for free or for a fee, or which may bepre-installed on a computing device or electronic device, or which maybe otherwise transported to and/or installed on such computing device orelectronic device.

Functions, operations, components and/or features described herein withreference to one or more embodiments of the present invention, may becombined with, or may be utilized in combination with, one or more otherfunctions, operations, components and/or features described herein withreference to one or more other embodiments of the present invention. Thepresent invention may thus comprise any possible or suitablecombinations, re-arrangements, assembly, re-assembly, or otherutilization of some or all of the modules or functions or componentsthat are described herein, even if they are discussed in differentlocations or different chapters of the above discussion, or even if theyare shown across different drawings or multiple drawings.

While certain features of some demonstrative embodiments of the presentinvention have been illustrated and described herein, variousmodifications, substitutions, changes, and equivalents may occur tothose skilled in the art. Accordingly, the claims are intended to coverall such modifications, substitutions, changes, and equivalents.

BIBLIOGRAPHY/REFERENCES

The following publications are hereby incorporated by reference in theirentirety; and embodiments of the present invention may optionallycomprise or utilize any components, systems, methods and/or operationsdescribed in any of the following publications:

-   1. T. Allen, Particle Size Analysis, John Wiley & Sons; ISBN:    0471262218; June, 1983.-   2. W. Tscharnuter, B. Weiner and N. Karasikov, TOT theory.-   3. R. Piestun, and J. Shamir, “Synthesis of three-dimensional    light-fields and applications” Proc. IEEE, Vol. 90(2), 220-244,    (2002).-   4. R. Piestun, and J. Shamir, “Control of wavefront propagation with    diffractive elements,” Opt. Lett., Vol. 19, pp. 771-773, (1994).-   5. B. Spektor, R. Piestun and J. Shamir, “Dark beams with a constant    notch,” Opt. Lett., Vol. 21, pp. 456-458, 911 (1996).-   6. R. Piestun, B. Spektor and J. Shamir, “Unconventional Light    Distributions in 3-D domains,” J. Mod. Opt., Vol. 43, pp. 1495-1507,    (1996).-   7. R. Piestun, B. Spektor and J. Shamir, “Wave fields in three    dimensions: Analysis and synthesis,” J. Opt. Soc. Am. A, Vol. 13,    pp. 1837-1848, (1996).-   8. M. Friedmann and J. Shamir, “Resolution enhancement by    extrapolation of the optically measured spectrum of surface    profiles,” Appl. Opt. Vol. 36, pp. 1747-1751, (1997).-   9. R. Piestun, B. Spektor and J. Shamir, “Pattern generation with    extended focal depth,” Appl. Opt., Vol. 37, pp. 5394-5398, (1998).-   10. N. Stanley-Wood, Roy W. Lines, Particle Size Analysis, The Royal    Society of Chemistry, ISBN: 0851864872, 1992.-   11. Alfred M. Bruckstein, David L. Donoho, Michael Elad: “From    Sparse Solutions of Systems of Equations to Sparse Modeling of    Signals and Images”, SIAM Review (2009)—Society for Industrial and    Applied Mathematics, Volume 51, Number 1, pages 34-81,

1.-56. (canceled)
 57. An optical system for particle detection, theoptical system comprising: (a) a flow cell for flowing a fluidcontaining particles along a flow direction; (b) an optical source forgenerating a beam of electromagnetic radiation in a propagatingdirection; (c) a beam shaping optical system positioned to receive thebeam of electromagnetic radiation; the beam shaping optical system forgenerating an anamorphic beam comprising a top hat beam and fordirecting at least a portion of the top hat beam through the flow cell;(d) first and second forward-looking detectors each configured to detectlight that has interacted with the one or more particles in the flowcell, wherein the first detector is configured to detect light from afirst region of the flow cell thereby generating a first signal, and thesecond detector is configured to detect light from a second region ofthe flow cell positioned down stream of said first region along saidflow direction, thereby generating a second signal; (e) an analyzer forreceiving the first signal from the first detector and the second signalfrom the second forward looking detector; wherein the analyzer generatesa differential signal from the first signal and the second signalcharacteristic of the particles.
 58. The optical system of claim 57,wherein: interaction of the top hat beam and the one or more particlesproduces light transmitted, scattered, or both, along the propagatingdirection; wherein at least a portion of said light transmitted,scattered, or both, along the propagating direction is detected by thefirst forward-looking detector and the second forward-looking detector.59. The optical system of claim 57, wherein said optical sourcecomprises a laser and the beam shaping system comprising a diffractiveelement for generating said anamorphic beam.
 60. The optical system ofclaim 57, wherein the anamorphic beam comprising said top hat beam ischaracterized by different optical powers in more than one spatialdimension.
 61. The optical system of claim 57, wherein the anamorphicbeam comprising said top hat beam is characterized by different opticalpowers in two spatial dimensions corresponding to a cross-sectional areaof the flow cell.
 62. The optical system of claim 57, wherein theanamorphic beam passes through the flow cell once.
 63. The opticalsystem of claim 57, wherein the anamorphic beam is directed to interactwith the first and second regions of the flow cell twice.
 64. Theoptical system of claim 57, wherein the anamorphic beam is directed tointeract with the first and second regions of the flow cell more thantwice.
 65. The optical system of claim 57, wherein the first and secondforward-looking detectors comprise one or more segmented linear detectorarrays.
 66. The optical system of claim 57, wherein the first and secondforward-looking detectors together comprise a segmented linear detectorarray.
 67. The optical system of claim 57, wherein the differentialsignal is the difference between the first signal and the second signal.68. The optical system of claim 57, wherein the analyzer generates asummation signal from the first signal and second signal characteristicof the particles, wherein the summation signal is the sum of the firstsignal and the second signal.
 69. The optical system of claim 57,wherein said analyzer analyzes said differential signals in a timedomain.
 70. The optical system of claim 57, wherein said analyzer countssaid one or more particles based on said differential signals.
 71. Theoptical system of claim 57, wherein said analyzer characterizes the sizesaid one or more particles based on said differential signals.
 72. Theoptical system of claim 57, wherein said analyzer comprises a patternmatching unit, to perform a pattern matching of (i) an array ofsynthetically generated potential interactions, with (ii) thedifferential signals.
 73. The optical system of claim 57, wherein saidanalyzer compares each differential signal with a pre-generated libraryof known signals corresponding to particles to determine if eachdifferential signal corresponds to a particle detection event or lasernoise.
 74. The optical system of claim 57, wherein each differentialsignal is converted to a frequency domain using a Fourier transformationor a fast Fourier transformation by said analyzer.
 75. The opticalsystem of claim 72, wherein the pattern matching is performed using aconvolution of the differential signal against a bank of variable delayand variable width matched filters according to equation (1):y _(k)(t)=x(b)*h _(k)(t)  (1) wherein x(t) is the differential signal;h_(k)(t) is a specific matching filter normalized to unit energy; andy_(k)(t) is an output signal.
 76. The optical system of claim 75,wherein a mean sensor response is represented by equation (2):$\begin{matrix}{{f_{\sigma,m}(t)} = {{\frac{d}{dt}e^{- {(\frac{t - m}{\sigma})}^{2}}} \cong {{- 2}( \frac{t - m}{\sigma} )e^{- {(\frac{t - m}{\sigma})}^{2}}}}} & (2)\end{matrix}$ wherein f_(σ,m)(t) is the mean sensor response, m is adelay parameter, σ is a width parameter, t is a time parameter, andamplitude values are ignored.
 77. The optical system of claim 76,wherein the anamorphic beam comprises two interacting lobes wherein atotal filter response h_(σ,m)(t) is represented by equation (3):$\begin{matrix}{{h_{\sigma,m}(t)} = {{{f_{\sigma,m}(t)} - {f_{{- \sigma},m}(t)}} \cong {{{- ( \frac{t - m}{\sigma} )}e^{- {(\frac{t - m}{\sigma})}^{2}}} + {( \frac{t + m}{\sigma} )e^{- {(\frac{t + m}{\sigma})}^{2}}}}}} & (3)\end{matrix}$ wherein each interacting lobe is assumed to be symmetricaround zero, f_(σ,m)(t) and f_(−σ,m)(t) are the mean sensor responsesfor each interacting lobe, m is the delay parameter, σ is the widthparameter, and t is the time parameter.
 78. The optical system of claim72, wherein a set of matched filters h_(k)(t) is generated, wherein kdescribes a certain pair {mk, σk}, each filter is designed with m and σparameters for positive and negative data channels, an absolute value ofeach output signal y_(k)(t) is computed, a maximum output signal iscompared with a threshold, parameters of the filter that created themaximum output signal above the threshold are employed as indicators form and σ, amplitude is taken from maximal y_(k)(t), and optionally ahistogram is computed and/or generated.
 79. The optical system of claim57, wherein the flow cell is removably integrated with the opticalsystem.
 80. The optical system of claim 57, further comprising anisolator provided between the optical source and the flow cell.
 81. Theoptical system of claim 57, comprising a diffractive optical elementprovided between the optical source and the flow cell.
 82. A method fordetecting particles in a fluid, the method comprising: (a) flowing thefluid containing particles along a flow direction through a flow cell;(b) providing a beam of electromagnetic radiation from an opticalsource; (c) generating an anamorphic beam comprising a top hat beam fromsaid beam of electromagnetic radiation and directing at least a portionof the top hat beam through the flow cell using a beam shaping opticalsystem; (d) detecting light that has interacted with one or moreparticles in the flow cell using first and second forward-lookingdetectors, wherein the first forward-looking detector is configured todetect light from a first region of the flow cell thereby generating afirst signal, and the second forward-looking detector is configured todetect light from a second region of the flow cell positioned downstream of said first region along said flow direction, therebygenerating a second signal; (e) an analyzing the first signal from thefirst forward-looking detector and the second signal from the secondforward-looking detector to generate a differential signalcharacteristic of the particles.
 83. The method of claim 81, wherein:interaction of the top hat beam and the one or more particles produceslight transmitted, scattered, or both, along the propagating direction;wherein at least a portion of said light transmitted, scattered, orboth, along the propagating direction is detected by the firstforward-looking detector and the second forward-looking detector. 84.The method of claim 81, wherein the differential signal ischaracteristic of the size of the particles.